The present invention relates to a device and a method for determining the ignition angle of an internal combustion engine.
In the BOSCH Technical Information, Kombiniertes Zxc3xcnd-und Benzineinspritzsystem MOTRONIC (Combined Ignition and Gasoline Injection System MOTRONIC) (1987 722 011, KH/VDT-09.85-De), control units for electronic ignition control are described, where between two ignition processes, the control unit ascertains the optimal ignition angle from engine information such as load, speed and temperature with reference to program maps. The ignition angle may thus be adapted individually to various operating states of the engine. The ignition angle may be advanced or retarded by any value as desired as a function of switching signals.
The German Published Patent No. 196 51 238 describes an ignition control system which contains a limiting module that limits the ignition angle, determined in light of engine information, to a maximally retarded value. Limitation of the ignition angle to a maximally retarded value is desirable, since in response to the demand for a torque reduction or a reduction in the thermal efficiency, the ignition angle may be retarded. However, the retarded ignition angle thus obtained may not exceed a maximally retarded value, since otherwise a permissible manifold temperature or a limiting value for emissions may be exceeded. According to the related art, such a maximally retarded value, the so-called static combustion limit (IASTAT(max)), may be determined in terms of the limiting value for the emission of hydrocarbons and the limiting value for the manifold temperature.
During certain operating states of the engine, secondary reactions may occur in the exhaust, so-called backfirings, which are caused by unburned or partially burned fuel getting into the exhaust. The backfirings may lead to noise pollution and destruction of components. The static combustion limit lies at ignition angles which are too retarded for the specific operating states.
A device and method, respectively, of the present invention may have the advantage that, during specific operating states, by advancing the maximally retarded ignition angle, exhaust backfirings and therefore noise pollution and destruction of components may be effectively avoided.
Advantageous further refinements and improvements of the device and method for determining the ignition angle are possible via exemplary embodiments and/or exemplary methods of the present invention. In particular, an exemplary method may be used for operating states in which an engine dynamic exists, and there is no positive engagement between the engine and the drive train. It may be advantageous to shift the maximally retarded ignition angle in the advance direction with reference to a static combustion limit which is a function of a program map, since this permits an even more targeted adaptation to engine parameters. It may also be advantageous to advance the ignition only in a specific period of time after determining the dynamic without positive engagement, during which exhaust backfirings actually occur, in order to quickly make the entire ignition-angle range available again for an adjustment of the ignition angle. It likewise may prove to be advantageous to observe a waiting time after detecting the dynamic without positive engagement, so that a maximum ignition-angle range may still be made available over a longer period of time. For the same reason, it may be advantageous to cancel the ignition advance of the maximally retarded ignition angle immediately after detecting a positive engagement between the engine and drive train. Since the occurrence of exhaust backfirings is temperature-dependent, it may be advantageous to make the amount of the ignition advance, as well as the waiting time and the period of time in which the ignition advance is carried out temperature-dependent. For the same reason, it may be advantageous to take the quantity of secondary air blown into the exhaust tract into account for the amount of the ignition advance. This may be carried out with a small expenditure of memory, since the quantity of secondary air is taken into consideration with the aid of a weighting factor.
Another operating state in which exhaust backfirings may be avoided by a shift of the maximally retarded ignition angle in the advance direction occurs during the post-start. Here, a reduction in the emission of hydrocarbons may be achieved by the advance of the maximally retarded ignition angle, as well. It may prove to be advantageous to lead the advance shift of the maximally retarded ignition angle during the post-start slowly to the steady-state combustion limit, in order to prevent sudden torque changes. In the same way, it may advantageous to make the period of time, in which the maximally retarded ignition angle is led to the steady-state combustion limit, a function of the engine temperature and the quantity of secondary air blown into the exhaust tract, since the leading may thus be carried out in a manner that it is adapted optimally to the engine parameters, and an unnecessary ignition advance is avoided. Given a selection of a linear leading-to function of the maximally retarded ignition angle, the computing expenditure may be advantageously minimized. It may be also advantageous in the selection of the advance of the maximally retarded ignition angle during the post-start to take into account whether measures have been taken to heat the catalytic converter, for because of the influencing of temperature associated with them, they may cause an increased occurrence of backfirings in the exhaust.